Known in the art of a device for preparation of an intravenous filter for implantation, which comprises a conducting catheter, a catheter introduction system, a filter fixing hook and a filter holding hook.
The filter holding hook is passed through the catheter, caught by a corresponding hook on the filter holder and the filter is pulled into the catheter, whereupon the filter is ready for implantation (cf. a prospectus of the firm Cook entitled "Gunter vena cava filter set" No. 600.4.85).
One more state-of-the art device for preparation of an intravenous filter for implantation is known to comprise a guide element having a cylindrical portion and a conical portion, as well as an applicator provided with a capsule for accommodating an intravenous filter, a conducting catheter connected to said capsule, a stylet and a collet grip. The stylet is accommodated inside the catheter and capsule and has a screw for the filter to be retained (U.S. Pat. No. 3,540,431).
To prepare the filter for implantation the stylet is passed through the capsule and catheter with its plain unthreaded end forward, whereupon the filter is screwed onto the stylet thread and is introduced, through the conical portion of the guide element, into its cylindrical portion, with the result that the filter gets folded up. Then the hole of the capsule is brought in register with that of the cylindrical portion, and the filter is made to move into the capsule, by virtue of retrograde traction of the stylet, and the capsule is withdrawn, together with the filter, from the guide element. The assembly procedure terminates in locking the stylet in position by means of the collet grip.
Implantation of an intravenous filter enclosed in any heretofore-known device is possible only through the right internal jugular vein, that is, by the so-called "retrograde" technique. Besides, to fold up the filter requires much effort to be applied, while its introducing into the capsule is fraught with damages to the filter construction, which are likely to be the cause of repeated thromboembolism of the pulmonary artery.
It is not infrequently that the intravenous filter is implanted, with the aid of the known device, in an angular position with respect to the longitudinal axis of the vena cava inferior, and the angle of inclination owes its origin from the fact that the applicator capsule has not been centred with respect to the vena cava inferior. Hence, an inclined position of the filter will result in its wrong unstable arrangement, which might be the cause of repeated thromboembolism of the pulmonary artery or proximal filter migration.